(1) Field of the Invention
The present invention relates to an image forming apparatus that includes a rotatable image carrier and a cleaning member which is in contact with a surface of the image carrier.
(2) Related Art
Image forming apparatuses such as copiers that are able to form color images include so-called tandem-type image forming apparatuses. Tandem-type image forming apparatuses have a structure such as follows: photosensitive drums for colors of, for example, C (cyan), M (magenta), Y (yellow), and K (black) are arranged along an intermediate transfer belt; toner images formed on the photosensitive drums are primarily transferred in a sequential manner onto the surface of the rotating intermediate transfer belt to be superimposed at a same position; and the toner images for the respective colors primarily transferred onto the surface of the intermediate transfer belt are collectively secondarily transferred onto a recording sheet.
According to the above-described structure, it is desirable that the entirety of the toner images on the intermediate transfer belt is secondarily transferred onto the recording sheet. However, in reality, part of the toner images remains on the surface of the intermediate transfer belt without being transferred. Accordingly, a cleaning unit for cleaning the toner remaining on the intermediate transfer belt (residual toner) is provided at a position that is downstream, in the belt moving direction, relative to the secondary transfer position.
One example of such a cleaning unit is an electrostatic-adsorption type cleaning unit whose cleaning brush applied with a bias voltage abuts onto the surface of the intermediate transfer belt and which electrically removes the residual toner by adsorbing it to the cleaning brush. The residual toner adsorbed to the cleaning brush is collected by a collection roller provided adjacent to the cleaning brush.
In a case of using this electrostatic adsorption method, the residual toner remaining in the cleaning brush (attached to the bristles of the brush) cannot be kept attracted to the cleaning brush without application of a bias voltage to the cleaning brush. Accordingly, if the intermediate transfer belt is rotated without the application of the bias voltage, the bristles of the brush abutting the belt surface move mechanically due to the rotation of the intermediate transfer belt, and this movement causes the residual toner remaining in the brush to come out toward the belt surface, smearing the belt surface by attaching thereto. Thus, a control is performed such that the bias voltage is applied to the cleaning brush first, and after that, the rotation of the intermediate transfer belt starts. However, such a control, that is, applying the bias voltage to the cleaning brush when the intermediate transfer belt is not rotating, causes the bias voltage to be continually applied from the start of the voltage application until the start of the rotation of the intermediate transfer belt. This leads to accumulation of unnecessary electric charge at the intermediate transfer belt at its belt portion which abuts against the cleaning brush.
The cleaning unit may have a smoke prevention seal for preventing toner smoke provided at its end portion in the downstream in the belt moving direction; and in a vicinity positioned downstream relative to the cleaning unit in the belt moving direction, a filming preventive member made of foam sponge may be provided in contact with the surface of the intermediate transfer belt, in order to scrape off external additives and the like of the toner which the cleaning brush could not remove. Consequently, once the intermediate transfer belt starts rotating, when the belt portion having the unnecessary electric charge remaining thereon passes by the smoke prevention seal and the filming preventive member, the toner having been attached to the smoke prevention seal and the filming preventive member is attracted by the charge remaining at the belt portion and may move to the belt surface, smearing it as a result.
Such a problem occurs not only to intermediate transfer belts, but also may occur to structures having a cleaning member that electrically removes residual toner on an image carrier, such as a structure using a photosensitive drum as the image carrier.